Compatibility with aiida v3 API

[dantogni]

Need refactoring of existing workflows to make aiida-kkr plugin compatible with the future aiida v3 API. Deprecated functions are still available in the current aiida version but will be removed in v3.

[Irratzo]

Relevant links.

• (For any issue) https://github.com/JuDFTteam/aiida-kkr/blob/master/CONTRIBUTING.md
• AiiDA Changelog - v2.0.0. URL.
  • This is where most of the namespace restructuring (i.e., API refactoring) that is relevant here, took place. Use this as reference to find all required changes.
• AiiDA 2.0 Migration Guide. URL.
  • This guide uses, among other things, the aiida-upgrade packages that should catch and correct most of these v2 API changes automatically.

For the record, I think that @PhilippRue already did most of this v2 update stuff (run the upgrade package etc.). So, I am a bit confused as to which updates need to be done.

So, it also could be that changes further up the AiiDA version list happened (see changelog). But I would be surprised, because usually "breaking changes" like these are only applied in major version changes (vX.0.0), not minor ones (vX.Y.0).

David mentioned these API changes so far that need to be updated. All of these, so far, are listed in the v2.0.0 API changes in the AiiDA changelog linked above.

• In combine_imp workflow and maybe others, please check:
  • .get_outgoing .get_incoming --> .base.links.get_outgoing, .base.links.get_incoming
  • On Dict Data objects: .get_attribute --> .base.attributes.get